Archaeology Magazine Archive

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Wind-Powered Furnaces Volume 49 Number 5, September/October 1996
by Brett Leslie Freese

As early as the seventh century A.D. Sri Lankans made steel in furnaces powered by monsoon winds, a previously unknown ancient technology. Forty-one iron-smelting furnaces have been found at a site in the arid region of Samanalawewa, according to Gill Juleff, director of the excavations for Sri Lanka's Archaeological Department.

Archaeologists had rejected the possibility of wind-driven furnaces because they believed that air blowing into them would not be sufficiently constant to sustain the high-temperature charcoal fires needed for smelting. To test this assumption, Juleff and her team built two replica furnaces based on the remains of those found at the site. Smelting trials revealed that monsoon winds blowing over the tops of the furnaces' front walls caused air to be drawn through conduits into the furnaces at a continuous rate. About half of the metal produced in these trials was high-quality steel.

Juleff says at least 76 other smelting sites identified in the region indicate that "the scale of operations went far beyond any village-based local activity." An estimated annual output of ten tons of steel from these sites was possibly traded in the Indian Ocean region. Sri Lankan steel, mentioned in ninth-century Islamic literature, may have been used for the blades of Damascus swords. Carbon-dated charcoal indicates that the furnaces were used until the eleventh century A.D.

© 1996 by the Archaeological Institute of America